Parenting and Collections trouble

I am new and very bad in english but I will try to explain the situation I am facing right now. I have some pieces of chess set the pawns are parented to an empty object and the empty object is parented to another empty object that collect all the other pieces of same color. That’s seems to working well and look like that:

Now I want to parent both White and Black pieces Empty to the board so I just click on the Empty White Pieces object first, then CTRL + Select the Board and CTRL + P , object (keep transform). Seems all ok but when I go check I missing in the list some PAWN and some pieces too, but if I do right click and select hierachy on the Chess Board.001 object then all the objects are selected properly ! But the funniest happen in this video
I just delete and undo random time a piece that not shown in the child list it magically appears. If I save and reopen then file the piece still not appear in the list … that’s happen to someone others I hope not just me because I’m getting crazy on this.